Psychotropic medications are a mainstay of effective treatment for bipolar disorder, but many patients fail to adhere to their medication regimens, for reasons including side effects and nonresponse. In many cases, timely medication adjustments could avert this non-adherence, but appropriate medication adjustments are not made, a phenomenon known elsewhere in medicine as 'clinical inertia'. Thus, dealing with clinical inertia could improve medication adherence. This study aims to provide information about the current extent of clinical inertia, its predictors, and its impact on medication adherence among patients with bipolar disorder (BD), in order to identify areas for possible improvement. In addition, we hypothesize that reducing clinical inertia would increase spending on medication costs, since greater adherence would prolong treatment. However, we hypothesize that this increase in medication costs would be more than offset by savings on hospitalization and other health care costs. The study aims are to: 1) Measure the extent and predictors of clinical inertia in medication treatment of BD. Specifically: a) to measure the proportion of visits in which no medication adjustment occurs, overall and specifically where an adjustment appears clinically indicated, and b) identify which patient and physician characteristics predict pharmacologic treatment adjustment at each visit following establishment of initial regimen. 2) Measure the association between clinical inertia (measured as lack of medication adjustment where indicated) and the degree of medication adherence. Identify what rate of treatment adjustment is associated with the highest level of medication adherence. 3) Determine whether increased use of clinically indicated medication adjustments would reduce total health care costs, despite increasing medication costs. The study aims will be accomplished through analysis of data from two naturalistic multi-site clinical trials of treatment for BD: the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD), and the Lithium Moderate Use Study (LiTMUS). These datasets include detailed longitudinal information on patients' clinical status and prescribed medications at each visit. The study will help to understand the extent of and effects of clinical inertia, a problem that has not been systematically studied for BD despite recent findings for other diseases. To the extent that clinical inertia contributes to medication non-adherence, our results will lay the basis for future interventions to address this problem.